(a) Field of the Invention:
The present invention concerns a device for controlling the movement of a pickup arm in a linear tracking pickup arm apparatus such as record or video disc player.
(b) Description of the Prior Art:
Known linear tracking pickup arm apparatuses are arranged so that, when a record disc or a video disc carried on a platter is played, a pickup arm is caused to progressively more linearly and radially of the disc, while being held tangential relative to the signal-carrying groove of the disc to allow a stylus or pickup tip of the pickup cartridge mounted at the foremost end of the pickup arm to progressively trace the signal groove toward the center of the disc. A general arrangement of such devices for controlling the movement of the pickup arm in known linear tracking pickup arm apparatuses comprises a servo system including a mechanism for detecting a horizontal offset angle of the moving pickup arm caused by the groove-tracing stylus and a mechanism for causing the pickup arm supporting carriage to travel in parallel with the direction of movement of the stylus to compensate for any offset angle detected by the detecting mechanism, to thereby always keep the pickup arm tangential to the signal groove of the disc.
Such linear tracking pickup arm apparatus requires the provision of means for disabling the servo system of the pickup arm movement controlling device whenever it is intended to move the pickup arm in a required direction in its upwardly pivoted position, when the user wants to make a quick return of the pickup arm to its initial position in the midst of playing or upon completion of playing of the disc, or when the user wants to bring the stylus to the lead-in position, or when the user wants to manually move the pickup arm by his fingers.
FIG. 1 shows an example of arrangement of a known device for controlling the movement of a pickup arm, designed to effect the disablement of the servo system. Reference numeral 1 represents a mechanism for detecting a horizontal offset angle of a pickup arm, designed to make this detection through a so-called photo-electricity converting system comprising a slit-carrying shutter plate 2 having a slit 2a and adapted to rotate horizontal in accordance with any horizontal swing of the travelling pickup arm, a light-emitting element 3 such as light-emitting diode disposed on one side of the slit-carrying shutter plate 2 and a pair of light-receiving elements 4a and 4b such as CdS photo-cells which are disposed on the other side of the shutter plate 2 to normally receive the light beam of the light-emitting element 3. Any horizontal displacement of the pickup arm is adapted to generate a change in voltage across resistors connected to the light-receiving elements to form a bridge circuit with the light-emitting element. The resulting output voltage of this offset angle detecting mechanism 1 is compared with a reference voltage in an operational amplifier 5, and its output is supplied to a first drive control circuit 6 for a motor 9 assigned to drive the pickup arm.
The first drive control circuit 6 for the motor generates a motor drive signal in accordance with an output of the operational amplifier 5, and delivers this signal to a contact point 7a of a changeover switch means 7. Suppose now that the record disc is being played, i.e. that the pickup arm head is in its lowermost position. A movable contact piece 7c of this switch means 7 is then in contact with the contact point 7a. Accordingly, the motor drive signal of the first drive control circuit 6 is supplied to the motor 9, causing this motor to rotate to move the pickup arm supporting carriage along a travel passageway, so that the pickup arm is driven while being corrected of its offset angle. On the other hand, in case a pickup arm quick return signal is generated by an autoreturn control circuit 10, or in case a manual operation command signal for the pickup arm is generated by a manual operation control circuit 11, such signal is supplied to a second drive control circuit 12 for the motor 9. On the basis of this signal, the second drive control circuit 12 delivers a motor drive signal to a contact point 7b of the switch means 7.
This changeover switch means 7 is arranged so that, with an upward tilting of the pickup arm, the connection of the movable contact 7c is switched from a contact point 7a to a contact point 7b. That is, when the completion of reproduction of the recorded signal of the disc is detected by a groove end sensor 13, or when a manual operation command signal for the pickup arm is detected by a manual operation detector 14, either one of these signals, as the case may be, is supplied to a solenoid drive circuit 15. Whereupon, this circuit 15 energizes a solenoid 16 to actuate its plunger to upwardly swing the pickup arm. When the pickup arm 17 is thus upwardly swung, a movable contact 18c of a changeover switch means 18 is switched of its connection from a contact point 18a to a contact point 18b, causing a transistor 19 connected to this switch 18 to be rendered conductive. Whereupon, a relay 20 connected to this transistor 19 is energized, so that the connection of the movable contact 7c of the switch means 7 is switched from the contact point 7a over to the contact point 7b. As a result, the motor drive signal of the second drive control 12 is supplied to the motor 9 to drive it in accordance with either the abovesaid quick return signal or the manual operation signal.
As stated above, the known pickup arm drive control device is arranged to be operative so that its relay 20 is energized in accordance with an ascension and a descension of the pickup arm 17 so as to change the connection of the changeover switch means 7 to transmit selectively an output signal of either the first drive control circuit 6 for sevo action or the second drive control circuit 12 for non-servo action to the motor 9 assigned to cause a travel of the pickup arm supporting carriage.
In such known device, however, a relay 20 is required as a means for effecting the switching of the connection of the changeover switch means 7. The employment of this relay has led to a complexity of the device and a cost-up of the apparatus as a whole.
In addition, such known linear tracking pickup arm apparatus as stated above has another problem when the pickup arm is to be moved manually utilizing the servo system. More particularly, in case the pickup arm of the apparatus is to be moved directly with the fingers of the user, the servo system has to be rendered to the enabled state, and the pickup arm is urged to move in a required direction to develop an output of the offset angle detecting mechanism, to thereby actuate the pickup arm moving mechanism. In such manual mode operation of the pickup arm using one's fingers, the pickup arm supporting carriage is allowed to move continuously by the servo system so long as the pickup arm is being urged by the user's fingers. Thus, there is the inconvenience that the pickup arm is moved beyond its limits of movement, causing an over-run of the pickup arm.
Furthermore, this known pickup arm apparatus having the above-mentioned arrangement has the following further inconvenience at the time of initiating the movement of the pickup arm. When this mechanism is about to drive the pickup arm, the servo system of the offset angle detecting mechanism is activated to be ready to detect any offset angle. Accordingly, in case at such moment the pickup arm is displaced to a substantial extent by an external force, a large angel is detected, and the pickup arm will be moved abruptly with a sudden great torque to result in an over-run of this arm.